diff --git a/testing/ostest/posixtimer.c b/testing/ostest/posixtimer.c
index e8fceab34..d5cd849bf 100644
--- a/testing/ostest/posixtimer.c
+++ b/testing/ostest/posixtimer.c
@@ -129,8 +129,8 @@ static void timer_expiration(int signo, siginfo_t *info, void *ucontext)
 
   if (oldset != allsigs)
     {
-      printf("timer_expiration: ERROR sigprocmask=%x expected=%x\n",
-              oldset, allsigs);
+      printf("timer_expiration: ERROR sigprocmask=%jx expected=%jx\n",
+              (uintmax_t)oldset, (uintmax_t)allsigs);
     }
 }
 
@@ -179,8 +179,8 @@ void timer_test(void)
     }
 
 #ifndef SDCC
-  printf("timer_test: oact.sigaction=%p oact.sa_flags=%x oact.sa_mask=%x\n",
-          oact.sa_sigaction, oact.sa_flags, oact.sa_mask);
+  printf("timer_test: oact.sigaction=%p oact.sa_flags=%x oact.sa_mask=%jx\n",
+          oact.sa_sigaction, oact.sa_flags, (uintmax_t)oact.sa_mask);
 #endif
 
   /* Create the POSIX timer */